Inspired by the published research on this site and comments on backpacking.net (and since I like to make most all of my own gear), I will make my own roll top dry bags. I plan to replace the relatively "heavy" webbing and nylon hardware with lighter cordage.

At one end of the top sack opening, a loop and a length of cord will be sewn. At the opposite end, just a loop will be sewn. After rolling down the top, the loose cord would first thread through the opposite loop, thread through the other loop, then pull taut. Around the taut cord between the loops, make a slip knot that is snug against the last loop the cord passed through. Two slip knots can be made for extra security. Click on picture to open a new window with a bigger image.

I am not sure about the stiffener material. But I will probably first try a 1" strip of polycarbonate (Lexan), 1/8" or thinner with the edges well rounded. A split-open piece of latex tubing can be fastened to the ends of the stiffener to further protect the bag fabric.

just a thought. i`ve found the plastic (nylon) from drink bottles to work great as a stiffener for belt pouches, etc, making them more user friendly. you can sew it to fabric (probably not very good for the needle) w/ a sewing machine. it`s cheap, light,& pretty tough stuff. ...slowhike

That bottle idea sounds like a good material. I choose the polycarbonate (aka Lexan) because I'm familar with working with it and I have a tablesaw and other equipement to easily tool it. But your suggestion makes me realize I can use 1/32" instead of 1/8". The thinner stuff would tool much like the plastic drink bottles. Scraps of polycarbonate can often be obtained for free from a plastic sheet supplier/fabricator.

Now I'm also thinking those flimsy food chopping mats could be used. It sews easy. Several layers can be sewn together to adjust the stiffness as needed. Same technique applies to the drink bottle material.

Thank you for the great tip. Much lighter!

And although most any cord can be used for my tie-top proposal, a thin, spectra cored cord lessens the weight too. The EZC Line sold through Gossamer Gear can hold a taught line hitch. So so it would hold slip knots. It's a lot strong - and more expensive - than necessary though.